Intercommunicating system



Oct. 12, 1948. R. H. HERRICK INTERCOMMUNICATING SYSTEM Filed Feb. 8, 1945 TO OTHER STA.

TO FIR ST SUBORDINATE STATION MASTER STATION TO OTHER STA.

" INT ENTIRE ROSWELL H. HERRIGK SUBORD l NATE STATI O N TO OTHER STA TO MASTER STATION ATTORNEY Patented Oct. 12, 1948 UNITED STATES PATENT OFFICE INTERCOMMUNICATING SYSTEM Roswell H. Herrick, Chicago, Ill., assignor to Automatic Electric Laboratories, Inc., Chicago, Ill., a corporation of Delaware Application February 8, 1945, Serial No. 576,787

9 Claims. 1

The present invention relates to telephone systems and more particularly to improvements in intercommunicating telephone and signaling systems of the type in which a loudspeaker is employed at a master station and the usual telephone instrument is used at each subordinate station.

The present invention is an improvement on my prior Patent No. 2,345,046, which was granted March 28, 1944, wherein an intercommunicating system of the character described is arranged in an improved manner to minimize all signal ener y losses in the signal transmission channels and to minimize the number of line conductors used to interconnect the stations.

It is an object of the present invention to provide an improved system of the character described which is arranged to prevent a subordinate station from eavesdropping on the master station.

Another object of the invention is to provide an improved circuit arrangement whereby a lesser number of conductors between subordinate stations are required.

A further object is to improve the transmission efficiency of the system by arranging to completely isolate the telephone instruments of the subordinate stations from the system when they are not in use.

The invention, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the following specification taken in connection with the accompanying drawing, in which:

Fig. 1 illustrates an improved intercommunicating system characterized by the features briefly referred to above.

Fig. 2 is a modification of Fig. 1 in which the common apparatus shown in Fig. 1 has been incorporated in the master station.

Fig. 3 is another modification of Fig. 1 in which the common apparatus has been incorporated in one of the subordinate stations.

Referring now to Fig. 1 of the drawing, the intercommunicating system there illustrated comprises a master station, a battery box, and one or more subordinate stations of which only one is shown. The system may, if desired, be used to provide communication facilities between the lobby and the several apartments of an apartment building, in which case the equipment of the master station is located in the lobby of the buildingand one of the subordinate stations is located in each apartment of the building. Alternatively, the system may be used to provide communication facilities between the ofiice of a business executive and the desks of his assistants.

Briefly considered, the equipment provided at the master station comprises a transmitter l, a loudspeaker 2, two condensers 3 and 4, two coupling transformers 5 and. 6, a resistor I, and a non-locking key 8. Each of the subordinate stations comprises a handset including a transmitter 9 and a receiver ill, a hook or cradle switch II, and a buzzer l2. The battery box, which contains apparatus common to all of the stations, comprises a transformer l3, a battery I4, two condensers l5 and I6, and two relays A and B. Separate channels are used for transmission and reception of voice signals at each station. More specifically, conductors 2| and 22 of line 2|] define a channel for the reception of voice currents at the master station, and conductors 22 and 23 define a second channel for the transmission of voice currents by the master station. Conductor 2| is also used in conjunction with conductor 24 to provide a circuit for controlling relay A from the master station. Conductor 22 is also used in conjunction with conductor 24 to provide a circuit for energizing the transmitter l at the master station. Similarly, conductors 3| and 32 of line 39 define a channel for the transmission of voice currents by the subordinate station, and conductors 32 and 33 define a second channel for the reception of voice currents at the subordinate station. Conductor 32 is also used in conjunction with conductor 34 to provide an operating circuit for the buzzer [2.

In considering the operation of the system it may be assumed that a call, intended for the subordinate station which has been illustrated, is initiated at the master station. In this regard it is noted that code signaling is utilized to selectively signal the ubordinate stations. Signaling is accomplished by momentary operations of switch 8. Each time that this switch is closed a circuit is completed to relay A, this circuit extending from negative battery through a winding of transformer [3, over conductor 2|, through switch 8, over conductor 24 and through relay A to positive battery. Relay A operates each time switch 8 is operated and completes a circuit from plus battery, through a winding of transformer.

l3, through contacts BI and A2, over lead 34, through buzzer I2, and back to negative battery over lead 32. Circuits to the buzzers of the other subordinate stations are completed over similar circuits. When thus energized, the buzzers operate to signal the subordinates. Since, however,

the switch 8 is operated in accordance With the code designating the illustrated station, only this station will answer the call.

Incident to the operation of the buzzers, a return signal is transmitted to the master station to indicate that the called station is being signaled. Thus as buzzer I 2 operates the contacts thereof are intermittently opened to-interrupt the current flow through the right hand winding of transformer I3. The pulsating current thus produced induces an alternating voltage in the left hand winding of transformer I3. This alternating voltage is impressed on the primary winding of transformer over conductors 2;] and 22 and through condensers 4 and L5. The resulting alternating current flowing in the primary winding of transformer 5 causes a corresponding alternating voltage to be induced in the secondary winding which voltage is reproduced by theloude speaker 2 as an audible return signal. 4

Whengthe attendant at the subordinate station answersthe call by lifting the handset 9, Ill-from its supporting hook or cradle, a circuit is completed for energizing transmitter 9:from the positive terminal of battery IA through a wi-ndingof transformer l3 and relay B, over conductor 31, through the upper contacts of switch ll, transmitter 9, and back to the negative terminal of battery 1.4 over lead .32. Coincident with the closure of this circuit the lower contacts of the hook or cradleswitch .|.l are closed to bridge the receiver Ifl'acrossthe line conductors 32 and 33. Relay B, being energized in series with transmitter 9, operates and at its contacts BI opens one point inthe operating circuit for the signaling buzzers such as 1.2; and at its contacts B2 completes a circuit for energizing transmitter l at'the master station. The'latter circuit may be traced from the positive terminal of battery 14, through relay A, ov-er conductor 24, through resi'stor l, transmitter I 'andone winding of transformer .6 to conductor 22 and thence returning to the negative terminal .of battery 14 through contacts B2. Relay A is adiustedso that it will not operate over the above traced circuit'but will holdover this circuit if operated. Theattendant at the subordinate station speaks intotransmi-tter 9 in answer to the call. The varying resistance of transmitter 9.causes an undulating current to 110W over the previouslytraced energizing circuit for the transmitter thus causing a corresponding alternating voltage to be inducedin the left hand winding of transformerv it, which voltage is impressed on the loudspeaker 2 over thepreviously traced circuit. The condenser I6 shunted across the winding of relay B provides a low impedance path for the undulating voice currents produced by the operation of transmitter 9. The party at the master station, upon hearing the attendant at the subordinate station answer, momentarily operates switch 8 to bring about theoperation of relay A as previously described. Relay A will not release when switch 8 is opened since it is held over the energizing circuit for transmitter I which was completed by the operationof relay B. Contacts A2 of relay A are now ineffective but the operation of contacts Al transfers conductor 23 from conductor 22 to conductor 33. A short circuit is thus removedfrom the secondary winding of transformer .6 and this winding is connected directly to receiver!!! over conductors 22, 32,33 and 23. With the system thus conditioned for; operation, an undulating .current flows through .the primary winding of transformer 6 whenever the resistance of transmitter I is varied by the party at the master station speaking into it. Condenser 3 increases the magnitude of the current undulations, for a given change in the resistance of transmitter I, by tending to maintain the total voltage across transmitter I and the primary winding of transformer 6 constant. The current undulations in the primary winding induce a correspondingailternatingvoltage in the secondary winding of transformer 6. This latter alternating voltage is impressed on receiver H) for aural reproduction. When the conversation is completed and the handset 9, i0 is restored on the hook or cradle switch II the circuit for energizing transmitter S in series with relay B is mterrupted. Relay B thereupon restores and opens the circuit-for energizing transmitter l and and reconnects conductor 23 to conductor 22 at contacts .Al.

The manner in which another subordinate station included in the system may be called and conversational circuits set up between suchanother station .and thegnaster; station .will be readily apparent in viewto'fl the for oin -explanation.

Since relay-Amaybesoperated. onlyby vtheoperation of switch'B- at the master station, and fur!- ther since contacts 'Al of relay A are arranged to normally disable the transmission channel for conveying voice signals :from themaster station to the subordinatestations, it is impossible for an attendant at asubordinate station to eavesp on the masters tiom Lif n the handset at a subordinate statiiln .energi'zesthe transmitter thereat and causes relayBto operate which in turn energizes the transmitterat.thema-ster station. but. without efiectsincethe secondary .wind-,

ing of transformer Bis normally short-.circuited and furthermore is normally disconnected from conductor .33. The party. atthe. subordinate station will be able to call the party at the master station by speakinginto the -.transmitter .9, The party at the master station maythenmomentary Operate switch} he wishes to reply. As

previously noted, relay A is .mat ined so as, to

prevent it from operating in. series with resistor 1, transmitter. LT and the primary winding of transformer 6 thouehi .11 hold oVer this circuittonce it has heenonlerateidby thev closure of switch 8. a

Since the signaleurrent transmission channels described .above do'not include amplifiers, the greatest possible. efficiency is required-to obtain anadequate loudspeakeravoiume from the sig*-- nal currents produced by: the transmitters provided at the subordinatestartions, and also to obtain adequate handset receiver volume from the master station transmitter l When-it is required that this transmitter shall respond to sound waves originatingat points -two:or three feet removed therefrom." TQDbtfiiI-liih required volume of re roduction atiboth th master-station and the subordinate stations theimpedancesbetween the various connected elements are carefully matched .andtlie iineilossesare held.

toa minimum.

The operation of the modified arrangementsshown in Figs. 2 and 3 isidentica1 to that [de scribecl for Fig. 1, the-.onlydifference being in the location of the equipmentishown in the battery box in Fig, 1. Thewhoiceof circuitsdepends upon the relativeflocations of-the several stations. Usual y .0116. Of; the circuits-will require a shorter tater-Length of iinethan the. others. .It should be apparent .that' in-case the subordinate stations real; with n h ar ns'range of each other that only a single buzzer, such as 12-, will be required. In this case the buzzer can be located at a central location, which may be in the battery box, and only three leads need then be run to the subordinate stations.

While particular embodiments of the invention have been disclosed, it will be understood that various modifications may be made therein which are within the true spirit and scope of the invention. I

What is claimed is:

1. In an intercommunicating system, a pair of stations each including a transmitter and a receiver, a four conductor line extending between said stations, the first and second conductors of said line defining a signal channel for coupling the transmitter at one station to the receiver at the other station, the second and third conductors of said line defining a signal channel for coupling the transmitter at the other station to the receiver at said one station, said one signal channel being normally disabled, means controlled over the second and third conductors of said line by said other station for energizing the transmitter at said one station over the second and fourth conductors of said line, and means controlled over the second and fourth conductors of said line by said one station for enabling said one signal channel.

2. In an intercommunicatin system, a pair of stations each including a transmitter and a receiver, interstation circuits providing a pair of signal channels between said stations, one of said signal channels coupling the transmitter at one station to the receiver at the other station and the other of said signal channels coupling the transmitter at the other station to the receiver at said one station, said one signal channel being normally disabled, a signal device, a key at said one station, means responsive to initial operation of said key for operating said signal device to call the other station, means responsive to an answer by the other station for energizing the transmitter at said one station, said first means being responsive to a subsequent operation of said key to enable said one signal channel for the duration of the call.

3. In an intercommunicating system, a pair of stations each including a transmitter and a receiver, interstation circuits providing a pair of signal channels between said stations, one of said signal channels coupling the transmitter at one station to the receiver at the other station and the other signal channel coupling the transmitter at the other station to the receiver at said one station, said one signal channel being normally disabled, a marginal relay for enabling said one channel, means controlled by the other of said stations for completing an energizing circuit to the transmitter of said one station in series with said relay, said relay being margined so as not to operate, but to hold when operated, over the transmitter energizing circuit, means at said one station for operating said relay to enable said one channel, said relay being held over the transmitter energizing circuit to maintain said one channel enabled for the duration of the call.

4. In an intercommunicating system, a pair of stations each including a transmitter and a receiver, common apparatus, a first line having at least four conductors extending between one of said stations and said common apparatus, a second line having at least three conductors extending between said common apparatus and the other station, the first and second conductors of said lines defining a signal channel for coupling the transmitter at one station to the receiver at the other station, the second and third conductors of said lines defining a second signal channel for coupling the transmitter at the other station to the receiver at said one station, said first signal channel being normally disabled, means controlled over the second and third conductors of said second line by said other station for energizing the transmitter at said one station, and means controlled over the third and fourth conductors of said first line by said one station for enabling said first signal channel.

5. In an intercommunicating system a pair of stations each including a transmitter and a receiver, a signal deviceat one of the stations, common apparatus, a first four conductor line extending between said one station and said common apparatus, a second four conductor line extending between said common apparatus and the other station, the first and second conductors of said lines defining a signal channel for transmitting signal currents between said stations in one direction, the second and third conductors of said lines defining a second signal channel for transmitting signal currents between said stations in the other direction, the fourth and one of the other three conductors of said first line defining a circuit for operating the signal device at said one station, and the fourth and one of the other three conductors of said second line defining a circuit for controlling the operation of said signal device from the other station.

6. In an intercommunicating system, a pair of stations each including a transmitter and a receiver, common apparatus, a first line having at least three conductors extending between one of said stations and said common apparatus, a second line having at least four conductors extending between said common apparatus and the other station, the first and second conductors of said lines defining a signal channel for transmitting signal currents between said stations in one direction, the second and third conductors of said lines defining a second signal channel for transmitting signal currents between said stations in the other direction, the second and fourth conductors of said second line defining a normally incomplete circuit for energizing the transmitter at said other station, and means controlled by said one station for completing said circuit.

7. In an intercommunicating system, a pair of stations each including a transmitter and a receiver, a signal device at one of said stations, a four conductor line extending between said stations, the first and second conductors of said line defining a signal channel for transmitting signal currents between said stations in one direction, the second and third conductors of said line defining a second signal channel for trans mitting signal currents between said stations in the other direction, the second and fourth conductors of said line defining a normally incomplete circuit for energizing the signal device at said one station, and means at the other of said 7 Times: defining a. channel: for transmitting voi'c'e currents betw'een saidi stations in one: direction the second. and third conductors of said-"lines defining a second channel for tran'smittingvoiee currents between said stations in the other direction, the second and fourth conductors of said: first linedefining a circuit for operating the signa-l'deviee at said onestation, and the first and fourth conductors of said second lineLdefining a: circuit for controlling. the operation of said-signal 10 device'from the other station. 7

9: man intercommunicating system, a pairof stations each including a transmitter and a receiver, interstation conductors linking said Sta:- tions',a signal-devicea key at one of said stations, means operatedin-respon'se to the operation of said-key, to energize said signal device to call 15, Number the other stationmeans responsive to an answer by theother station foren'ergizing the transmither at said one stationwithoutrenderine it efiec five; said'first-means subsequently operated in response to the: operation ofxsai'd key, to render effective the transmitter thereat: for the direction of the call.

ROSWELL HERRICK.

REFERENCES CITED The fol1owing references are of" record in the file-of thispatent:

UNITED: STATES PATENTS- 7 Name Date LS-1195228 Williams-etala Mar, 1, 1927 2, 02,903 Leveqiie Dec; 21, 1937 

